1. Field of Invention
The present invention relates to gas analyzers which operate on the principle that at a given wave length, photons are absorbed by a gas in direct proportion to its concentration. By transmitting infrared rays through a sample chamber and reading the same through a filtered detector, the drop in the output of the detector is calibrated to the concentration reading of the gas, such as carbon monoxide (CO) or unburned hydrocarbons (HC). Such instruments appear in Class 250, Subclass 43.5.
2. Description of Prior Art
The prior art is best set forth in Chapter 10 of Mullard, pages 129-142, the book title being:
Applications of Infrared Detectors, printed in 1971, by Wightman and Co., Ltd., London SW9 6DS, England To be noted in particular with regard to the proposals made by Mullard, particularly on page 132, Figures A, B, and C, is the disclosure of a reference tube and a sample tube, and yet the discussion of a prototype beginning at page 136 relates only to a single tube unit. The problems encountered in the field, particularly in garages where temperature variables in cold weather can be between 70.degree. and -40.degree.C, illustrated the futility of using a single gas sample tube without a reference chamber. Furthermore, the unit shown is capable of reading for only one gas or ingredient at a time, whereas automotive emissions standards proposed require the simultaneous reading for CO and unburned HC since the two are to a degree interrelated in the adjustments required to reduce the concentration to acceptable levels. Where commercial units have been developed, such as illustrated in U.S. Pat. No. 3,562,522, they have been slow to warm up, such as one-half hour to an hour. In addition, continued variables have required almost constant tuning. Also lacking commercially is an inexpensive unit which will read out more than one gas or component simultaneously.